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This page contains 3 independent sections, "Simulation setup", "Find and plot mode SSb0", and "Effective index as a function of waveguide thickness". The first section describes how to set up the simulation file. You can skip this step, by downloading the associated plasmon.lms file from the top-level Plasmonic Waveguide page and proceeding to the second section. Section 2 describes how to find the SSb0 mode and plot the field profiles. Section 3 describes how to set up a sweep to obtain the effective index as a function of waveguide thickness.

Simulation setup

 

Start a new simulation. Since we are using a 2D Z-normal Eigenmode solver you can open the simulation up in 2D drawing mode by selecting the menu options below. This hides the z dimension since we are not using it.

 

gs_plasmon_2d_drawing_mode_zoom88

 

Add new material to material database

Press on the MATERIAL database button icon_materials to open the material database

Click on the Add button and select (n,k) material. This adds a new material named "New Material 1" to the database. Edit this material according to the following table.

property

value

Name

Ag Berini :: 633nm

Refractive Index

0.0607893

Imaginary Refractive Index

4.35932

 

Set up structure and MODE Solver region

Press on the arrow on the STRUCTURES button icon_structures and select a RECTANGLE from the pull-down menu.  Set the properties according to the following table.

tab

property

value


name

waveguide

Geometry

x (μm)

0


x span (μm)

1


y (μm)

0


y span (μm)

0.1


z (μm)

0


z span (μm)

1

Material

material

Ag Berini :: 633nm

Press on the arrow on the SIMULATION button icon_mode_simulation and select a EIGENMODE SOLVER region. Set the properties according to the following table.

tab

property

value

General

solver type

2D Z normal


background index

2

Geometry

x (μm)

0


x span (μm)

2


y (μm)

0


y span (μm)

0.6


z (μm)

0

Mesh Settings

mesh cells x

200


mesh cells y

60

Boundary Conditions

x min bc

Symmetric


x max bc

Metal


y min bc

Anti-Symmetric


y max bc

Metal

Press on the arrow on the SIMULATION button and select a MESH region icon_sims_override. Set the properties according to the following table.

tab

property

value

General

set mesh multiplier

yes


x mesh multiplier

100


y mesh multiplier

100

Geometry

x (μm)

0.5


x span (μm)

1e-7


y (μm)

0.05


y span (μm)

1e-7


z (μm)

0

 

 

Find and plot mode SSb0

Open the analysis window by pressing on the RUN button icon_run.

First press the MESH STRUCTURE button to mesh the structure, and obtain a spatial plot of the refractive index

In the MODAL ANALYSIS section set the properties according to the following table. Then press CALCULATE MODES. The effective index of plasmon modes is often higher than the maximum real part of the effective index. For this reason we want to search for a n which is higher than the default "use effective index" setting.

property

value

wavelength (μm)

0.633

number of trial modes

5

search

near n

use max index

uncheck

n

2.5

There are 3 different methods which can be used to create the plots of the ssb0 mode

Analysis Window

You can plot the components of the profile using the mode plot options of the analysis window. See the mode plot options page in the reference guide for more details.

Script File

Open the script file editor, as shown on the MODE GUI page of the Introduction section. Next, press on the OPEN button icon_open_script  and browse to the plasmon_plot.lsf script file included in the installation directory for MODE or on the first page of this example. Then press on the RUN SCRIPT button icon_run_script . The script will generate the plots on the previous page.

Visualizer

In the analysis window, the mode data appears in a list with mode numbers. Find the mode of interest and select it in the Object tree as shown below. Choose to Visualize the electromagnetic fields.

gs_plasmon_visulize_zoom90

 

You can then select which components of the E field data you want to plot in the Visualizer. The screenshot below shows how to plot the real part of the z component of the Electric fields.

gs_plasmon_reez_visualizer_zoom86

 

 

 

Effective index as a function of waveguide thickness

 

Step 1: Make mode1 data available to parameter sweep

We are interested in obtaining the effective index and loss data from the ssb0 mode. Note that when we found modes in the previous step, the ssb0 was always the first mode in the mode list. In analysis mode we can see the mode1 data in the MODE data group (left image below). If you switch to layout (right image below), the mode1 data is no longer available. The first step is to make sure the mode1 data is available for the sweep.

 

gs_plasmon_editmodedatagroup_zoom97

 

Edit the MODE data group by right clicking on the object with your mouse. Select the Edit object option from the list.

In the Analysis->Variables tab click the bottom ADD button twice. This will add two results which the data group can give to the parameter sweep. Rename these two results "neff" and "loss" as shown in the bottom left window.

Switch to the Analysis->Script tab shown in the right part of the image below. Then add the following two lines of script commands which will add data to the "neff" and "loss" results once a simulation has run. Press OK to save your changes.

neff=getdata("mode1","neff");

loss=getdata("mode1","loss");

 

gs_plasmon_editmodedatagroup2_zoom94

 

Step 2: Create a sweep

Open the Optimization and Sweeps window using the VIEW menu at the top of the graphical user interface, or by right clicking on the top title bar of the MODE GUI.  

Press on the CREATE NEW PARAMETER SWEEP button icon_sweep to add a new sweep to the simulation. Right click on the parameter sweep and choose to Edit the parameter sweep. Set the properties according to the following screenshot. Notice that the only results you can chose are the results which are seen in the screenshot of the Analysis->Variables tab above.

 

gs_plasmon_thickness_sweep_zoom88

 

Step 3: Run the sweep and plot the data

Press on the RUN SWEEP button icon_run_sweep in the Optimizations and Sweeps Window to run the sweep.

Plot the sweep data using one of the methods below. The first method was used to create the plots on the previous page.

Script Prompt

Open the Script Prompt Window using the VIEW menu at the top of the graphical user interface, or by right clicking on the top title bar of the MODE GUI.

Copy and paste the following commands into the Script Prompt and press ENTER on the keyboard to execute them.

thickness = getsweepdata("thickness","waveguide_span");

neff = getsweepdata("thickness","neff");

loss = getsweepdata("thickness","loss");

 

# plot results

plot(thickness*1e6,neff,"Waveguide thickness (um)","effective index");

plot(thickness*1e6,loss*633e-9/(2*pi*20*log10(exp(1))),"Waveguide thickness (um)","loss (k)");

Visualizer

Right click on the parameter sweep and choosing what data to visualize, as shown in the image below. Note that the loss will be in dB/cm, and that the script commands above converted the units of the loss to k.

 

gs_plasmon_visualize_sweep_zoom94

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